Electrically conductive terminal means



March 16, 1965 A. S. LOUIS ELECTRICALLY CONDUCTIVE TERMINAL. MEANS Filed 001;. 19, 1962 42 |& as as FIG. 4

FIG. 3

INVENTOR ARNOLD S. LOUIS ATTORNEY United States Patent 3,174,126 ELECTRICALLY CONDUCTIVE TERMINAL BEANS Arnold S. Louis, 87 Southgate Ava, Hastings on Hudson, N.Y. Filed Oct. 19, 1962, Ser. No. 231,768 2 Claims. (or. 333-312) The present invention relates to an improved electrically conductive termination adapted to provide electrical connection between a molded conductive plastic element and a metal terminal, whereby electrical continuity is established without the necessity of conventional washer and solder means and without the use of mechanical anchoring means, such as spinning, riveting, or flaring the end of a terminal member over a washer. The present invention further relates to a process for forming such an electrical connection whereby several of the steps employed in the conventional method of manufacture are eliminated, and a simplified, low cost and highly reliable termination device is provided. More particularly, but not limited thereto, the invention is useful in providing a connection to the resistive element of a potentiometer.

In potentiometers of the type where a resistive track is for-med on an insulator base, terminals are positioned proximate to the resistive track and passed transversely through the insulator block. On certain such potentiometers conductive paints are commonly employed to provide electrically conductive paths on the surface of the insulator base block to make electrical connection between the resistive element and a terminal pin. Connection between the conductive paint path and the terminal pin is usually made by means of a washer disposed about the projecting portion of the pin and overlying an area of conductive paint. Electrical continuity between the paint and the pin relies in considerable measure on a mechanical pressure contact between the washer and the paint. It is a particular advantage of this invention that a comolded bond is provided between the conductive path and a conductive plastic member in which there is insert molded the terminal pin. Thus a mechanically secure connection is obtained. On the other hand, in the prior art construction, the projecting portion of the pin was peened against the washer by riveting or spinning, to anchor the washer. In addition to this mechanical contact, a layer of solder is conventionally deposited over the flattened terminal pin head and the washer, to insure electrical continuity. it will be appreciated that these two steps in the manufacturing process involve expensive and time-consuming assembly operations. Further, it is necessary to employ highly skilled personnel to carry out the operations, which involve fairly close tolerances in very limited areas. Improper riveting or spinning may cause overtight connection with the possibility of breakage of parts, while a loose connection will provide an improper seat for the application of the solder. This prior art solder connection has, in general, proved incompletely reliable. It will be appreciated that the elimination of these two steps in the manufacture of the device will not only substantially reduce the cost of the unit but will eliminate a frequent source of malfunction, thus greatly reducing the number of rejects upon inspection and providing a more reliable potentiometer device.

The present invention is particularly adapted to be used with potentiometers of the type wherein a conductive plastic resistance track is formed integrally with a plastic insulator base by a comolding process. The eomolding manufacturing step employed for forming the resistive track may also be used to form the takeoff means. In a preferred form of the invention the heat and pres sure utilized in the comolding operation is also employed to simultaneously provide a molded connection from the 3,174,.l2ti Patented Mar. 16, 1965 resistance element and takeoff means to the termination means of this invention.

As will be explained in detail hereinafter, a secure low resistance connection is provided by this invention which obviates the need for soldering, spinning, or otherwise mechanically deforming the terminal.

It is therefore a primary object of the present invention to provide an improved terminal means.

it is a particular object to provide a termination comprising a metal terminal member molded into a conductive plastic member.

It is a different object to provide an electrically conductive path comolded to a termination means.

Still a further object is to provide an improved potentiometer.

It is another object of the present invention to provide a highly simplified terminal device characterized by the absence of a mechanically deformed terminal pin, or a washer, and of the need for soldering such a pin to a washer It is a further object of the present invention to provide a simplified manufacturing process whereby electrical devices employing molded conductive elements may conveniently be constructed.

A further object of the present invention is to provide a potentiometer termination characterized by a high degree of reliability and simplicity of construction.

These and other objects and aims of the present invention will be pointed out with particularity or will become apparent from the following description and the figures appended thereto, in which:

FIG. 1 is a perspective sectional view of a portion of a potentiometer employing the termination of the present invention.

FIG. la is a section taken in elevation showing prior art means for securing a terminal pin to a molded conductive path.

FIG. 2 is a plan view of the mold member used in the manufacture of the device of the present invention showing recesses loaded with conductive materials.

FIG. 3 is a cross-section taken along lines 3-3 of FIG. 2.

FIG. 4 is a fragmentary View in vertical cross-section of a compression mold in position for simultaneously comolcling a resistive composition, a termination means, and an insulator block.

Referring now more particularly to the drawings, there is shown in FIG. 1 a view of the device of the present invention characterized generally by the numeral 10, wherein conductive plastic resistive track 12 is formed on insulator block 14 by comolding means to be described in detail hereinbelow. Terminal pin 16 having end portion 22 is also secured thereon at the time of comolding. A knurled pin is preferred as it provides positive anchorage.

A pair of electrically conductive wipers 17a, 17b, traverse resistance track 12 and takeoff 15. An electrioally conductive member 19 interconnects wipers 17a and 1715. A terminal pin 16 is connected to resistance track 12 by means of a molded conductive path 18. As will be more fully described hereinafter, a novel termination is provided between the terminal pin and conductive path l8.

As shown in FIG. la, the prior method for such connection involves positioning washer 20 about the end portion 22 of a terminal pin 16. Portion 22' is then riveted or peened against washer 20 to form a tight mechanical contact, which is then covered with solder 24 to insure electrical continuity. It is to be noted that if tight mechanical contact is not obtained, then poor or unreliable electrical connection may result. It will be appreciated that an imperfect soldering job is unreliable 3 and can introduce added resistance to the circuit or even an open circuit.

From consideration of FIG. 1, it will be appreciated that the device of the present invention eliminates washe 2d and also deformation of the end portion 22 of the terminal pin to. That is, no stress such as riveting or spinning has been imparted to the device, with consequent risk of damaging parts. There is also an absence of solder, which was used in the older method and which has inherent weaknesses.

By way of example, the invention will be described hereinafter as applied to the manufacture of a molded conductive plastic potentiometer of the rotary type. As shown in FIG. 2, the molding process utilizes a mold member 24 which is formed with a number of grooves in the face thereof. In annular recess 26 there is deposited a conductive plastic resistive powder This powder is adapted to form the resistive track 12 upon comolding. in the portion of the recess between the end terminals an insulator plastic powder is used as a filler.

"While the embodiment herein illustrated by way or" eirample is that of a circular, or rotary, potentiometer, rectilinear potcntiometers may also be formed using similar means.

A second groove 3b has deposited therein a powdered metal slurry 29 of highly conductive material such as powdered or flake ilver, or the like, with a minor proportion of resinous binder. It is preferred that the binder be con posed of the same resin as is the insulator base. Groove 3d intersects groove 26; thus the slurry 29 forms an electrical contact with the conductive powder 23 at this point. The other end of groove 38 terminates in a rounded recess 32, whereby the slurry 29 forms a thin rounded disc at this point. This is shown in FIG. 2, taken in conjunction with FIG. 3, which for clarity has omitted conductive powder 23 and slurry 29. A highly conductive plastic composition 31 is also deposited in annular groove 33 to form the takeoff track 15. With resistive composition 2% and slurry 29 deposited in the respective grooves, mold member 24 is assembled in a simple compression mold comprising mold member 24-, an upper mold force 34, and a collar member 35. Mold member 24 functions as the lower force. An insulator plastic compact, or preform, which becomes base 14 after molding, is juxtaposed above the surface of mold member 24, as shown in FIG. 4. This compact, or preform, is composed of particle of a moldable synthetic resin material compressed to an extent which enables it to retain its shape prior to the molding process. Transverse apertures 36 are formed in member 24, these apertures being provided with enlarged recessed rim portions 37 which are adapted to provide seats for annular inserts 39. Inserts 39 are compacts or preforms of highly conductive plastic, such as disclosed in US. Patent 2,761,854.

The raised track construction described hereinabove is disclosed more fully in U.S. 2,760,719 which is assigned to the assignee of this application. The invention is also applicable to resistance elements which are molded flush with the surface of the base.

Insert 39 may be readily impressed into seat 3"! and a frictional fit will retain it in position. As shown in PEG. 1, the bore it? of insert 39 is of a narrower diameter than that or" aperture Metal pin to is passed through aperture 36, pin ltd being maintained in spaced relationship to base 14; by means of radial flange 42 formed on pin to which acts as a stop member. If desired, insert may extend completely through member As shown in FIG. 4, base 14 serves as the mounting means for terminal pins 16 and inserts 39. After member 14 is positioned, the mold in juxtaposition with the loaded mold member 24 is inserted in a conventional hydraulic press having heated platens, and molding is l carried out at the normal temperature and pressure for the particular resin employed.

The terminal pin is shown with a projecting portion merely by way of illustration. The pin may be terminated in conductive member 39.

As shown in PEG. 1, resistive track 12 and insert 39 are then comolded with insulator base 14. The conductive slurry forms a highly conductive path 18 from the resistive element 12 to conductive insert 39 which, in turn, is molded to end portion 22 of terminal pin 16. It will be noted that the need for solder is eliminated, as is the need for mechanical deformation of the terminal since the conductive plastic insert makes excellent contact to both terminal pin and slurry deposit.

There has thus been provided in accordance with the present invention, a unitary structure whereby electrical connection is made between a molded conductive pathand a metal terminal pin, characterized by the absence of soldering and riveting operations.

As used herein, comolding is the molding together of two or more plastic deformable materials under conditions of heat and pressure which produces deformation of the materials resulting in a monolithic intermingled closely bonded structure. A comolded structure can be identified by an intermingled configuration of the interface between a pair of moldable materials which have been joined by comolding.

While it is preferred to employ a conductive slurry having the resin constituency as the insulator base so that a strong unitary structure is obtained by molding, for less critical applications conventional resin based conductive paints may be used for the formation of the conductive path. The basic advantage of the conductive member 39 will still be obtained.

While the invention has been described in connection with a potentiometer or resistive device, it is equally applicable to switching devices and other devices employing a molded conductive path.

There has been disclosed heretofore the best embodiment of the invention presently contemplated and it is to be understood that various changes and modifications may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

l. A potentiometer element including:

an insulator plastic base provided with a conductive plastic member comolded thereto;

a terminal pin having a portion thereof in said conductive plastic member and a respective end portion disposed externally of said base and said conductive plastic member;

a conductive plastic resistance element formed on said base and affixed thereto in cornolded integral relationship; and

a conductive composition strip formed on said base and registering with said resistive element in electrical connection therewith, said conductive strip also registering with said conductive plastic member in electrical connection therewith.

2. The element of claim 1 wherein said conductive composition strip is comolded to said base and said conductive plastic member.

References Cited by the Examiner UNITED STATES PATENTS 1,950,750 3/34 Ruben 338308 2,169,594 8/39 Schellcnger 338-308 2,269,136 1/42 Tellkamp 338312 X 2,679,569 5/54 Hall 338-308 X 2,700,719 1/55 Coler et a1 338308 X 2,873,336 2/59 Tassara 338-174 X RiCHARD M. WOOD, Primary Examiner. 

1. A POTENTIOMETER ELEMENT INCLUDING: AN INSULATOR PLASTIC BASE PROVIDED WITH A CONDUCTIVE PLASTIC MEMBER COMOLDED THERETO; A TERMINAL PIN HAVING A PORTION THEREOF IN SAID CONDUCTIVE PLASTIC MEMBER AND A RESPECTIVE END PORTION DISPOSED EXTERNALLY OF SAID BASE AND SAID CONDUCTIVE PLASTIC MEMBER; A CONDUCTIVE PLASTIC RESISTANCE ELEMENT FORMED ON SAID BASE AND AFFIXED THERETO IN COMOLDED INTEGRAL RELATIONSHIP; AND A CONDUCTIVE COMPOSITION STRIP FORMED ON SAID BASE AND REGISTERING WITH SAID RESISTIVE ELEMENT IN ELECTRICAL CONNECTION THEREWITH, SAID CONDUCTIVE STRIP ALSO REGISTERING WITH SAID CONDUCTIVE PLASTIC MEMBER IN ELECTRICAL CONNECTION THEREWITH. 